Contents, like music, a moving image, a still image, and a text, that are in the form of analogue information are on their way to becoming handled as digitized data in a large portion of cases. A digital content of this type is not only used as its content itself but also as a content including a main body of the content and a program having a function of reproducing the content, or a game software content and the like.
The number of chances of a content being utilized by a network is also increasing with the advance of a network like the Internet. A system that is recently on its own way to become prevalent downloads a content by a network through use of an electronic device having a communication function, like a personal computer (PC), a portable phone terminal, a smart-phone, a portable information terminal, a game terminal, and a music playing terminal and utilizes the downloaded content.
A method for protecting copy right of a content by means of embedding copy right information in the main body of content data has been adopted as example management of copy right in connection with usage of a content. A method for adding copy right information includes a method for embedding a content ID into content data by use of an electronic watermark technique, or the like, a method for adding content information, like a DCD (Distributed Content Descriptor), into a content header, and others (see; for instance, Non-Patent Document 1).
In relation to management of copy right of a content, there has also been proposed a data communication system that stores information for identifying a proprietor into a header of content data and that allows only an authorized proprietor to reproduce a content, thereby protecting profits of a copy right holder (see; for instance, Patent Document 1). In order to safely distribute a digital content, another proposed system (see; for instance, Patent Document 2) sends a content to a user in an encrypted form; and decrypts and reproduces the encrypted content data by using key information and user authority information.
As a method for controlling communication over the network, there is a method controlling a connection between a sender and a receiver, to thus enable transmission of multimedia data by use of call control, like an SIP (Session Initiation Protocol). Proposed systems employing an SIP include a system that enables performance of transfer control according to header information, a system that enables billing of a phone or digital data, and the like (see; for instance, Patent Documents 3 and 4).